The present invention relates to devices for removing metal tubes from heat exchangers and surface condensers. More specifically, the invention relates to a device capable of both pulling a tube out of a heat exchanger, flattening the tube, and chopping the tube into smaller lengths for disposal.
Many heat exchangers utilize tubes for carrying a heat transfer fluid. A large number of tubes are commonly mounted in parallel between two tube sheets. The tube ends are tightly mounted in openings in the tube sheets, forming a tight seal. The tight fit is often effected using a press fit. A high temperature fluid such as combustion gas or hot water is passed between the tube sheets and around the outside of the tubes. A lower temperature heat transfer fluid such as water is passed through the interior of the tubes. Heat is transferred from the higher temperature tube exterior to the lower temperature tube interior.
Tubes often have to be removed from the heat exchanger. Tubes often become corroded, lined with scale or even plugged. Tubes also develop leaks, requiring tube removal. Heat exchanger downtime is often unexpected, and speed is critical in removing one or more tubes, replacing them with others, and returning the heat exchanger to service.
Heat exchanger preventative maintenance is often planned, with several or all tubes in an array being removed and replaced before leaks and severe scaling are likely to occur. In large power generation systems there may be thousands of tubes to replace during the same downtime interval, significantly reducing the power generating capacity while the preventative maintenance is being performed. The downtime in such situations is expensive, the expense depending on how quickly the tubes can be replaced.
Removing tubes from a heat exchanger is accomplished by first relieving the interference fit between the tube and tube sheet. The tubes are axially pulled out a few centimeters to expose a grippable tube end projecting from the tube sheet. Such pulling is accomplished with an internal gripping device called a tube puller. Suitable tube pullers are disclosed in commonly owned U.S. Pat. No. 3,835,520 or U.S. Pat. No. 3,628,246.
After the tube has been loosened and has an end projecting from the tube sheet, a pulling device is used to pull the tube totally out of the tube sheet. A typical pulling device comprises a pair of rotating serrated traveller rolls having parallel axes and rotating in opposite directions. The projecting tube end is introduced into the nip between the rollers. The puller rapidly removes the tube from the tube sheet. Prior art devices for removing long tubes from tube sheets axially at high rates of speed are disclosed in U.S. Pat. Nos. 3,149,021 (Curfman), U.S. Pat. No. 3,785,026 (Ohmstede), U.S. Pat. No. 4,044,444 (Harris) and U.S. Pat. No. 4,815,201 (Harris), the later two invented by the applicant.
The tube can be 10 to 20 meters long in large power installations. This rapidly moving tube typically requires two people to handle the tube as it is being pulled out of the tube sheet. After removal, the tube is feed to a chopper, to cut the tube into pieces to be hauled away as scrap. The use of typical tube pullers thus requires people to handle the withdrawn tube, a separate chopper, and people to feed the withdrawn tube to the chopper. Each additional step requires additional time as well as additional workers.
What remains to be provided is a tube puller which eliminates the need for a separate chopper. A tube puller which does not require additional workers to handle the long tubes being extracted would be desirable. It would also be advantageous to eliminate the safety considerations of maneuvering long tubes into nippers in power houses.
The present invention is a tube remover for extracting a tube from an opening in a wall in which the tube is mounted. The remover includes a nipper roll and an anvil roll. Each roll has, formed on a radially outward facing surface thereof, a plurality of teeth. Further, each roll is disposed for rotation about an axis. The axes of rotation are spaced from one another so that the rolls, together, define a nip within which the tube to be removed can be fed. The rolls are rotated in opposite directions and draw the tube into the nip and between the rolls. A cutting surface is provided on one of the rolls, and, as the cutting surface and teeth on the opposing roll cooperate to distress the pinched tube as it passes between the rolls, the tube is cut at a desired length.
In a preferred embodiment, the teeth formed on both the nipper roll and the anvil roll are helically oriented. The angle of helical disposition is such that, when the rolls rotate with respect to one another, the teeth mesh.
In the preferred embodiment also, teeth provided on the outwardly facing surface of the anvil roll are inclined at a designated angle. This enables more secure retention of the tube and more efficient drawing of the tube between the rolls.
Further, the preferred embodiment employs a nipper roll and an anvil roll which have different diameters. In consequence, the teeth on the nipper roll, as the nipper roll is rotated, engage different teeth on the anvil roll on subsequent rotations.